1. Field of the Invention
The present invention pertains to apparatus and methods for manipulating tubular members. More particularly, the present invention relates to well working apparatus for manipulating pipe members into and out of wells.
2. Description of Prior Art
Well working rigs of considerable variety are known, and include design features to achieve special purposes. For example, rigs are known with fold-down masts sufficiently lightweight to be transportable by truck to and from well sites. It is desireable, particularly for economic purposes, to be able to transport virtually an entire rig on a single truck, and to be able to configure the mast for operating on a well in a short period of time after arrival at the well site.
Workover rigs, for performing operations on already-drilled wells, are generally small compared to rigs used to initially drill wells, and may even take the form of a snubber, a gin pole and a winch line. Such workover rigs are generally transportable by truck. However, such workover rigs may be limited to manipulating a single pipe member at a time as opposed to a drilling rig which can typically manipulate a stand of three pipe members threaded together. Similarly, snubbers used to drive pipe into wells under high pressure well conditions, for example, generally grip and manipulate one pipe member at a time, and operate over a stroke length typically of just a few feet. Consequently, a workover rig, for example, should be operable to manipulate pipe members rapidly so as to minimize the time required to withdraw a pipe string from a well, or to insert a pipe string into a well.
U.S. Pat. No. 4,267,675, which was filed concurrently with the aforementioned application Ser. No. 35,933 and which was issued May 19, 1981, discloses apparatus and methods for extending and locking a mast. The Ser. No. 35,933 application discloses apparatus and methods for high speed manipulation of pipe by means of a double closed-loop chain-operated well rig, utillizing a pair of elevators, for example, to handle two separate pipe members simultaneously. The Ser. No. 258,923 application discloses apparatus and methods for high speed snubbing of pipe into wells, for example. Pipe gripping apparatus is disclosed for mounting on the double chain drive of the Ser. No. 35,933 application rig so that pipe may be driven into a high pressure well, for example, by reciprocal motion of the chain loops. The gripping assembly includes fluid pressure operated propulsion apparatus for manipulating pipe gripping slips, wherein the slips may be automatically locked in engagement with a pipe member.